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.TH UCLAMPSET 1 "August 2020" "util-linux" "User Commands"
.SH NAME
uclampset \- manipulate the utilization clamping attributes of the system or
a process.
.SH SYNOPSIS
.B uclampset
[options]
.RI [ -m\ uclamp_min ]\ [ -M\ uclamp_max ]\ command\  [ argument ...]
.br
.B uclampset
[options]
.RI [ -m\ uclamp_min ]\ [ -M\ uclamp_max ]
.B \-p
.RI pid
.SH DESCRIPTION
.B uclampset
sets or retrieves the utilization clamping attributes of an existing \fIpid\fR,
or runs \fIcommand\fR with the given attributes.

Utilization clamping is a new feature added in v5.3. It gives a hint to the
scheduler about the allowed range of utilization the task should be operating
at.

The utilization of the task affects frequency selection and task placement.
Only schedutil cpufreq governor understands handling util clamp hints at the
time of writing. Consult your kernel docs for further info about other
cpufreq governors support.

If you're running on asymmetric heterogeneous system like Arm's big.LITTLE.
Utilization clamping can help bias task placement. If the task is boosted such
that
.B util_min
value is higher than the little cores' capacity, then the scheduler will do its
best to place it on a big core.

Similarly, if
.B util_max
is smaller than or equal the capacity of the little cores, then the scheduler
can still choose to place it there even if the actual utilization of the task
is at max.

Setting a task's
.B uclamp_min
to a none zero value  will effectively boost the task as when it runs it'll
always start from this utilization value.

By setting a task's
.B uclamp_max
below 1024, this will effectively cap the task as when it runs it'll never be
able to go above this utilization value.

The full utilization range is: [0:1024].
The special value -1 is used to reset to system's default.

.SH OPTIONS
.TP
.B \-m
Set util_min value.
.TP
.B \-M
Set util_max value.
.TP
.BR \-a ,\  \-\-all-tasks
Set or retrieve the utilization clamping attributes of all the tasks (threads)
for a given PID.
.TP
.BR \-p ,\  \-\-pid
Operate on an existing PID and do not launch a new task.
.TP
.BR \-s ,\  \-\-system
Set or retrieve the system-wide utilization clamping attributes.
.TP
.BR \-R ,\  \-\-reset-on-fork
Set
.B SCHED_FLAG_RESET_ON_FORK
flag
.TP
.BR \-v ,\  \-\-verbose
Show status information.
.TP
.BR \-V ,\  \-\-version
Display version information and exit.
.TP
.BR \-h ,\  \-\-help
Display help text and exit.
.SH USAGE
.TP
The default behavior is to run a new command:
.B uclampset
.I [-m\ uclamp_min]
.I [-M\ uclamp_max]
.IR command\  [ arguments ]
.TP
You can also retrieve the utilization clamping attributes of an existing task:
.B uclampset \-p
.I pid
.TP
Or set them:
.B uclampset \-p
.I pid
.I [-m\ uclamp_min]
.I [-M\ uclamp_max]
.TP
Or control the system-wide attributes:
.B uclampset \-s
.I [-m\ uclamp_min]
.I [-M\ uclamp_max]
.SH PERMISSIONS
A user must possess
.B CAP_SYS_NICE
to change the scheduling attributes of a process.  Any user can retrieve the
scheduling information.

.SH NOTES
The system wide utilization clamp attributes are there to control the _allowed_
range the tasks can use. By default both
.B uclamp_min
and
.B uclamp_max
are set to 1024. This means users can set the utilization clamp values for
their task across the full range [0:1024].

.TP
For example:
.B uclampset \-s
.I -m\ 512
.I -M\ 700
.PP
will prevent any task from being boosted higher than 512. And all tasks in the
systems are capped to a utilization of 700. Effectively rendering the maximum
performance of the system to 700.

Consult your kernel docs for the exact expected behavior on that kernel.
.SH AUTHORS
.UR qais.yousef@arm.com
Qais Yousef
.UE
.SH SEE ALSO
.BR nice (1),
.BR renice (1),
.BR taskset (1),
.BR sched (7)
.sp
See
.BR sched_setscheduler (2)
and
.BR sched_setattr (2)
for a description of the Linux scheduling scheme.
.SH AVAILABILITY
The uclampset command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.
